A. aurantia with her recently
captured prey, a flower fly (family Syrphidae). The zig zag "writing"
below the captured fly gives this spider its common name of "Writing
Spider". Note also the spinnerets, visible as a brownish disk on
the spider's abdomen.

The largest orb-weaving spiders (family Araneidae) in
Wisconsin are two species in the genus Argiope
(pronounced ar-GUY-uh-pee), A. trifasciata
and A. aurantia (shown
here in ventral view). Females of the two species are easy to separate
by looking at the top of their abdomens. A.
aurantia
displays an elaborate pattern of yellow spots on black, andA. trifasciata’s abdomen is
crossed with numerous black, silver, and yellow stripes.

Both species are daytime predators that usually hang
head down in the center of their webs, which they often spin in fields
between tall grasses or forbs. Their web is distinctive not only for its
great size—dragonflies are often snared by them—but because
of the zigzag silk banding, called the stabilimentum,
that the spider decorates the center of the web with. Scientists argue
about the function of the stabilimentum (some evidence indicates it attracts
insects), but this gives the spiders one of their common names, “writing
spiders”. These species are the basis of the popular children’s
story about a literate spider, Charlotte’s Web. It was once held
in the southern United States that seeing one’s name written by
the spider presaged one’s death. In any case, the writing spider’s
web does indeed spell death for many flying and jumping insects of Wisconsin’s
fields, such as the flower fly (family Syrphidae) wrapped up in the upper
left corner of this photo (note the large red eyes).

Just before dying in the autumn, the females will produce
a single brown leathery egg sac, filling it with hundreds of eggs. The
spiderlings hatch, then spend the winter inside the sac. They emerge in
the spring and make small webs near the ground. As they grow through the
summer, the webs get larger and higher, and the web/spider combination
becomes conspicuous in August and September, before the first hard freeze
kills most of those who remain. The males are rarely seen except in the
vicinity of the female’s web; they are about 100 times smaller than
the females.